METHODS FOR THE MICROSCOPIC STUDY OF BACTERIA 221 



H H 



I I 



H C=O H C=O H C OH H C OH 



I I I I 



H C OH HO C H H C OH HO C H 



I I I I 



HO C H HO C H HO C H HO C H 



till 



H C OH H C OH H C OH H C OH 



I I I I 



H C OH H C OH H C OH H C OH 



I I I I 



H C H H C H H C H H C H 



I I I I 



o o o o 



H H H H 



D. Glucose. D. Mannose. D. Sorbite. D. Mannite 



The fermentation of these hexoses and their respective alcohols 

 by certain bacteria is shown in the accompanying table: 



Organism. D. Dextrose D. Mannose. D. Sorbite. D. Mannite 



B. dysenterise Shiga + + 



B. dysenteiise Flexner . + + + 



B. Morgan No. 1 . . . + + 



B. paratyphosus Beta + + + + 



An explanation for the phenomenon set forth in the table does not 

 readily suggest itself. Somewhat similar selective action upon specific 

 amino acids by other bacteria is known, qualitatively at least. Thus, 

 members of the Hemorrhagic Septicemia Group, particularly those 

 derived from animal sources, produce indol in plain broth media. 

 Typhoid bacilli, diphtheria bacilli and many other pathogenic organ- 

 isms usually fail to produce indol in ordinary media under similar con- 

 ditions. It is possible that this noteworthy action of members of the 

 Hemorrhagic Septicemia Group upon tryptophan may be related to 

 the fact that this amino acid is an important constituent of the hemo- 

 globin, the coloring matter of the blood; the Hemorrhagic Septicemia 

 Bacteria are particularly likely to grow in the blood stream of infected 

 animals. 



Fermentation reactions of bacteria in varied carbohydrate media 

 are of importance in their cultural identification. The table on page 

 316 illustrates the separation of members of the Intestinal Group of 

 Bacteria by their fermentation reaction in various carbohydrates. 



Milk. Milk is an important natural medium for bacterial growth. 

 It contains protein, carbohydrate and fat, together with inorganic 

 salts. A variety of reactions and changes in milk are produced by 

 bacterial development. 



